World War II Flak Tower Transformed Into Tropical Aquarium in Vienna

Structures built during wartime sometimes serve as haunting reminders of an era citizens would rather forget. Some of these buildings are demolished at the end of conflict, however others are adapted and given a new life. Flak Towers - anti-aircraft gun shelters originally built to protect the Third Reich - pose this issue, but one tower in the heart of Vienna, Austria has been transformed into a massive zoo and aquarium called the Haus des Meeres.

The blockhouse towers – enormous concrete and steel leviathans that dominated the skyline – were constructed in Berlin, Hamburg, and Vienna and used in defense against Allied air raids. Each one was built over the course of just six months, however they’re remarkably durable and feature three and a half meter-thick walls that served as air-raid shelters and sites the Luftwaffe used to defend the cities.

Today, Vienna’s Haus des Meeres could not be further displaced from this reality. Located in Esterhazy Park, the site offers views over the city, and the interior offers five floors of displays. A multi-story greenhouse has been constructed on the outside of the flak tower, complete with wooden walkways and rope bridges, and tropical vegetation that thrives amid small water features.

Inside, fish and turtles are on display while a variety of tropical birds and marmosets wander freely among the visitors. The Haus des Meeres also has a vivarium where visitors can find snakes, lizards, and crocodiles, and even a shark aquarium on the ground floor.

The Haus des Meeres is just one of the flak towers in Vienna, Austria. A complete list can be found at http://de.wikipedia.org/wiki/Wiener_Flaktürme (in german). I wanted to note, that of your photographs only one displays the Haus des Meeres, all the other pictures are from different towers.
All the towers actually come in pairs, one contained the command centre (Feuerleitstelle) and the other the actual gun crews (Gefechtsturm).
Others of the towers are used as depots, one is used as an exhibition room/centre for the Museum of Applied Arts in Vienna. Once there was a discussion to use one of them as a high security data centre, which is, btw, already the case with one other war relic in Austria.